We visited in Spain in October 2017 in 14 days - not counting arrival and departure days. We chose the Artrip in Madrid, because the hotel was within walking distance of the Atocha train station and the "Big 3" museums. A very nice 2*
http://www.artriphotel.com/en
I would highly recommend a few days in Seville. The Hotel Becquer is an affordable 4* within walking distance of all the major attractions in Seville.
http://www.hotelbecquer.com/en/
We had originally booked the Hotel Granvia in Barcelona, but when I needed to change the reservation, the room cost went over our budget, so we stayed at the U232 in the Eixample instead. The U232 worked out great for us. We walked everywhere except to Park Guell, and the meet-up place for our day tours.
http://www.u232hotel.com/en/